Modeling of gallium nitride transistors for high power and high temperature applications

Wide bandgap (WBG) semiconductors such as GaN and SiC are emerging as promising alternatives to Si for new generation of high efficiency power devices. GaN has attracted a lot of attention recently because of its superior material properties leading to potential realization of power transistors for high power, high frequency, and high temperature applications. In order to utilize the full potential of GaN-based power transistors, proper device modeling is essential to verify its operation and improve the design efficiency. In this view, this research work presents modeling and characterization of GaN transistors for high power and high temperature applications. The objective of this research work includes three key areas of GaN device modeling such as physics-based analytical modeling, device simulation with numerical simulator and electrothermal SPICE model for circuit simulation. The analytical model presented in this dissertation enables understanding of the fundamental physics of this newly emerged GaN device technology to improve the operation of existing device structures and to optimize the device configuration in the future. The numerical device simulation allows to verify the analytical model and study the impact of different device parameters. An empirical SPICE model for standard circuit simulator has been developed and presented in the dissertation which allows simulation of power electronic circuits employing GaN power devices. The empirical model provides a good approximation of the device behavior and creates a link between the physics-based analytical model and the actual device testing data. Furthermore, it includes an electrothermal model which can predict the device behavior at elevated temperatures as required for high temperature applications.Includes bibliographical reference

The Design, Simulation and Implementation of Inductively Powered Sensor Systems: New Applications, Design Methodologies and a Unique Coil Topology

Three case studies have been presented for new applications of inductive energy and data transfer (iEDT)-sensor systems. The first application is a condensation detection system for the windshield of an automobile. The developed iEDT-sensor prototype provides a low cost alternative for wireless dew point measurements which involves no wired connections and so can be easily replaced when the windshield is damaged. The second application involves an iEDT-sensor prototype developed wirelessly query the flow rate in a pipe. For the third application, measurement results were performed for a wireless implant system. The application involves a Wireless Sensor (WS), implanted under the dura mater, which was to be used for long term cortical measurement and stimulation with a very high resolution. A suite of tools provided two independent methods of simulating the coil self resonance, quality factor, coupling and self inductance as well as the overall system efficiency. The inductance and coupling were verified within 10% error compared to measurement results and the resonance, quality factor and efficiency to within 30% error. An accurate simulation of the efficiency was predicated by an accurate simulation of the quality factor at the operating frequency. A series of scripts were also developed to automate the construction of the coil geometry, the simulation control and the compilation of the simulation results. These scripts offered the ability to quickly analyze variations in implementation and their affect on the system parameters and efficiency. For the third application, a new and unique topology for the iEDT-sensor system was presented which resulted in three redundant and independent implant coils each capable of simultaneously delivering power to the sensor electronics. This phased array topology has never before been examined for iEDT-systems as far as is known by the author. The new topology demonstrated a similar efficiency when compared to a single implant coil system of the same dimensions and a similar quality factor. Upon implantation, simulations demonstrated that the expected loss in efficiency should be limited to 10%. SAR-value simulations showed that the ISM frequencies at or below 13.56MHz would be in compliance with FCC regulations. The coupling and self inductance measurements for the phased array coil system were confirmed within 10% error compared to the simulations and the quality factor, self-resonance and efficiency were also shown to be accurate to within 20%. The simulated maximum efficiency of the phased array system was, however, substantially lower than the analytically calculated efficiency due to parasitic effects. The outlook for the work is as follows. The scripts should be expanded to include inductors with magnetic cores in order to allow for high power and low frequency applications as well as 3-D simulations in order to allow for more complex geometries. It should also be possible to increase the efficiency per unit area of the phased array coil system by minimizing the parasitic impedance thereby leading to an efficiency per unit area that is greater than that of a single coil system. The result would be a higher efficiency system, especially important for high power applications. This type of phased array coil approach could also be employed in the coil system of the Wireless Power Supply in order to create large areas which could efficiently supply mobile wireless devices with power

Reliability Analysis of Power Electronic Devices

The thesis deals with the reliability of Power Electronic Devices to the purpose of evaluating the phenomena which mainly dictate the limiting conditions where a power device can safely operate. Reliability analyses are conducted by means of either simulations and experimental measurements